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cb0ae1fbb2
While trying NFSv4.0/RDMA with sec=krb5p, I noticed small NFS READ operations failed. After the client unwrapped the NFS READ reply message, the NFS READ XDR decoder was not able to decode the reply. The message was "Server cheating in reply", with the reported number of received payload bytes being zero. Applications reported a read(2) that returned -1/EIO. The problem is rpcrdma_inline_fixup() sets the tail.iov_len to zero when the incoming reply fits entirely in the head iovec. The zero tail.iov_len confused xdr_buf_trim(), which then mangled the actual reply data instead of simply removing the trailing GSS checksum. As near as I can tell, RPC transports are not supposed to update the head.iov_len, page_len, or tail.iov_len fields in the receive XDR buffer when handling an incoming RPC reply message. These fields contain the length of each component of the XDR buffer, and hence the maximum number of bytes of reply data that can be stored in each XDR buffer component. I've concluded this because: - This is how xdr_partial_copy_from_skb() appears to behave - rpcrdma_inline_fixup() already does not alter page_len - call_decode() compares rq_private_buf and rq_rcv_buf and WARNs if they are not exactly the same Unfortunately, as soon as I tried the simple fix to just remove the line that sets tail.iov_len to zero, I saw that the logic that appends the implicit Write chunk pad inline depends on inline_fixup setting tail.iov_len to zero. To address this, re-organize the tail iovec handling logic to use the same approach as with the head iovec: simply point tail.iov_base to the correct bytes in the receive buffer. While I remember all this, write down the conclusion in documenting comments. Signed-off-by: Chuck Lever <chuck.lever@oracle.com> Tested-by: Steve Wise <swise@opengridcomputing.com> Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com> |
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